An image processing system, which is used for processing and displaying an image of a target object, is implemented in various fields. The image processing system may include an image processing system for an ultrasound diagnosis (hereinafter referred to as “ultrasound diagnostic system”).
The ultrasound diagnostic system transmits an ultrasound signal from the surface of a human body toward a desired portion within a target object. This allows an ultrasound image of soft tissues or blood flow to be obtained through non-invasive means by using information obtained through ultrasound echo signals. Compared to other medical imaging systems such as X-ray diagnostic systems, X-ray CT scanners, MRIs and nuclear medicine diagnostic systems, the ultrasound diagnostic system is advantageous since it is small in size and fairly inexpensive. Further, the ultrasound diagnostic system is capable of providing a real-time display and is highly safe without any dangerous side effects such as exposure to X-rays, etc. Thus, the ultrasound diagnostic system is extensively utilized for diagnosing the heart, abdomen and urinary organs, as well as widely applied in the fields of obstetrics, gynecology, etc.
Reflectivity of the ultrasound signals in blood flow is different from that in a myocardium. The reflectivity of the ultrasound signal in blood flow is relatively low while its moving velocity is more rapid than myocardial velocity. On the contrary, although myocardial velocity is relatively slow, the reflectivity of the ultrasound signal in the myocardium is very high. By using such a disparity of reflectivity in blood flow and the myocardium, a component of ultrasound signals reflected from the blood flow may be removed so that the myocardial velocity may be measured. A tissue Doppler image (TDI) indicating the measured myocardial velocity may be used to evaluate a myocardial function.
The TDI may transmit ultrasound signals to a target object along one scan line with an identical acoustic field at a constant time interval, receive reflected ultrasound signals from the target object, and detect a phase shift of received ultrasound signals to thereby compute a mean Doppler frequency by using auto correlation. This enables a color image of the target object to be displayed. The TDI may be applicable for assessing objective systolic and diastolic myocardial velocities, determining regional dysfunction and quantitatively assessing the myocardial velocities. The TDI may be helpful in following up cardiac functions from congenital and acquired cardiac diseases.
To configure TDI receiving scan lines according to the prior art, an ensemble number of transmit scan lines of the same position are required for calculation. Further, an auto correlation is performed upon received signals to form the TDI. That is, the ultrasound signal is repeatedly transmitted to one scan line by the ensemble number N (e.g., N ultrasound transmissions to a first scan line, N ultrasound transmissions to a second scan line, N ultrasound transmissions to a third scan line . . . ). Then, the received signals are synthesized to produce the TDI. For example, assuming that 10 scan lines are required for one TDI, the ultrasound signal should be repeatedly transmitted to each of the scan lines by the ensemble number N (10 N ultrasound transmissions) such that it requires a long time to produce the TDI. Especially, a frame rate is determined depending on a region of interest, an ensemble number, an interleaving number and the like. The conventional method of producing the TDI repeatedly transmits the ultrasound signal to each scan line by the ensemble number. This increases delay with increasing ensemble number. This delay causes a problem in that the frame rate decreases.